What happened
The pilot intended to proceed to Mount St. Helens to land near Spirit Lake. The winds in the vicinity of the desired landing point were too strong for a safe landing. Therefore, an alternate spot was selected below the ridge line and presumably sheltered from the wind. Late in the approach hover, the aircraft began a sudden side drift which could not be arrested. The pilot reported that a strong gust of wind had blown the aircraft out over the back side of the ridge. He reported that when the helicopter moved out of ground effect, it began to settle and he was unable to stop the descent. The impact forces were sufficient to damage the aircraft beyond economical repair. The density altitude was about 6200 ft.
The investigation
The pilot's account indicates that the loss of control occurred during the transition from hover to forward flight or vice versa, specifically when the aircraft moved out of ground effect. The high density altitude of approximately 6200 feet likely contributed to the reduced performance capability of the helicopter in these conditions.
Findings
The primary factor was the strong gust of wind that pushed the helicopter over the ridge line. The inability to arrest the side drift and subsequent descent suggests a loss of lift or control authority at high density altitude. The damage sustained was consistent with an impact with terrain.